Asthma is a disease effecting approximately 20 million Americans. The death rates from asthma have increased substantially since 1979, increasing for children over five years of age from the period from 1979 to 1982. Hospitalization rates for asthma increased by 50% for adults in that period and by over 200% for the period from 1965 to 1983. Hospitalization rates for black patients are 50% higher for adults and 150% higher for children than the general population. (R. Evans et al., "National Trends in the Morbidity and Mortality of Asthma in the US," Chest (1987) 91(6) Sup., 65S-74S). Increasing asthma mortality rates for the same period of time has been documented in other countries. (R. Jackson et al., "International Trends in Asthma Mortality: 1970-1985," Chest (1988) 94, 914-19.)
The mainstay for the management of asthma as well as other respiratory diseases in the United States has been inhaled aerosolized medication. The primary aerosolized drugs currently prescribed for respiratory therapy in the United States are anti-inflammatory drugs, bronchodilators and enzymes. These medications can be self-administered by patients using hand held metered dose inhalers (MDIs). Bronchodilators, while useful for the management of an acute asthma attack, are currently not the preferred drugs of choice for long-term asthma management. Aerosolized anti-inflammatory drugs, such as inhaled steroids and cromoglycates, used in conjunction with objective measures of therapeutic outcome are the preferred tools for long-term management of the asthmatic patient. (U.S. Department of Health and Human Services, "Guidelines for the Diagnosis and Management of Asthma," National Asthma Education Program Expert Panel Report, pub. no. 91-3042, August 1991.)
Quantitative spirometry allows clinically relevant indices of pulmonary function to be followed in the asthmatic patient during therapy or for any patient suffering from a respiratory disease. Forced vital capacity, FEV.sub.1, peak expiratory flow and mid-expiratory values have all been shown to be useful for following the effect of respiratory therapy. (Quakenboss et al., "The Normal Range of Diurnal Changes in Peak Expiratory Flow Rates: Relationship to Symptoms and Respiratory Disease," Am Rev Resp Dis (1991) 143, 323-30; Nowak et al., "Comparison of Peak Expiratory Flow and FEV.sub.1 : Admission Criteria for Acute Bronchial Asthma," Annals of Emergency Medicine (1982) 11, 64-9.) Because spirometry involves recording several parameters with sensitive and complex instrumentation, the peak expiratory flow rate (PEFR) has been adopted as a useful index for inexpensively allowing patients to monitor their own pulmonary function at home. (Darman, "Pulmonary Function Testing; Use of the Peak Expiratory Flow Rate in an Outpatient or Office Setting," Journal of Asthma (1984) 21 (5), 331-37.) The use of objective assessment of pulmonary function for managing asthmatic patients is critical because patients and physicians tend to inaccurately assess the patients' own pulmonary conditions. (Shim et al., "Evaluation of Severity of Asthma: Patients versus Physicians," American Journal of Medicine (68), 11-13.) The inability of patients and physicians to recognize the signs of a severe asthma attack may be a factor contributing to the observed increasing asthma death rates. (Sears, "Increasing Asthma Mortality--Fact or Artifact?," Journal of Allergy and Clinical Immunology (1988) 82, 957-60.) Providing patients with peak expiratory flow measurement information may cause them to manage their own asthma more rationally. (Janson, Bjerkel et al., "Effect of Peak Flow Information on Patterns of Self-Care in Adult Asthma," Heart Lung (1988) 17, 543-49; Williams et al., "Expiratory Flow Rates: Their Role in Asthma Therapy," Hospital Practice (1982) 10, 95-110.)
A rational program for self-administration of aerosolized asthma therapeutic drugs would include: a) avoidance of overuse of bronchodilators, given that all bronchodilator drugs may be potentially toxic when used in excess (W. Spitter et al., "The Use of B-Agonists and the Risk of Death and Near Death from Asthma," N Engl J Med (1992) 326, 501-6); and b) using an anti-inflammatory drug on a prescribed scale which may include regular dosing several times a day (J. L. Malo et al., "Four-times-a-day Dosing Frequency Is Better than Twice-a-day Regimen in Subjects Requiring a High-dose Inhaled Steroid, Budesonide, to Control Moderate to Severe Asthma," Am Rev Respir Dis (1989) 140, 624-28).
It is a problem with peak expiratory flow rate monitoring that peak expiratory flow rate data is typically interpreted out of context with aerosolized drug dosing events. For example, a marginally acceptable peak expiratory flow rate data point with that peak expiratory flow rate measurement made one minute following the administration of a bronchodilator has a different meaning than if that same measurement with that same value were made one minute prior to the administration of an aerosolized bronchodilator drug.
It is a problem with peak flow monitoring when used to monitor the long-term therapeutic effect of anti-inflammatory aerosolized asthma therapeutic drugs that peak flow data must be interpreted in the context of aerosolized anti-inflammatory drug dosing events. For example, if the, patient's peak expiratory flow rate is deteriorating over a period of weeks when the patient is compliant with his anti-inflammatory aerosolized drug therapy program, this deterioration in objective lung function measurement has a very different meaning than if the patient is failing to take his medication as prescribed.
It is a problem with metered dose inhalers that the patient must record in his diary the time of each drug dosing event. It is a problem with portable peak expiratory flow rate measuring devices that the patient must record each peak flow measurement in a diary. There is a system available allowing metered drug dose inhaler drug dosing events to be automatically recorded. (Nebulizer Chronolog.) There is also an instrument available for printing out the time and value of a peak flow measurement made by a patient at home. It is a problem with these automatic dose logging devices and automatic peak expiratory flow rate logging devices that they do not intercommunicate to allow a definitive analysis of the relationship between drug dosing events and peak flow measurement events. In particular, small differences in the real time clocks contained within the dose logging device and peak flow logging device would make it impossible to determine the temporal relationship of drug dosing events and peak flow monitoring events. When acutely acting bronchodilators are used, a difference of even one or two minutes between the time-based standards used by the drug dosing logging device and the peak flow measurement logging device would introduce unacceptable error in evaluating the relationship of drug dosing and objective pulmonary function measuring events.
It is a problem with these logging devices that when used to monitor a chronic anti-inflammatory aerosolized drug asthma therapy program, the overall compliance of the patient is not easily evaluated. For efficient evaluation of patients in the office setting, an easy-to-read graphical display of long-term compliance with asthma therapy is essential in order to rapidly identify the non-compliant patient and, thus, correctly interpret peak expiratory flow rate data.